Pharmacokinetics and consistency of pericardial delivery directed to coronary arteries: direct comparison with endoluminal delivery

Exploring the role of pericardial miRNAs and exosomes in modulating cardiac fibrosis

The potential of the pericardial space as a therapeutic delivery tool for cardiac fibrosis and heart failure (HF) treatment has yet to be elucidated. Recently, miRNAs and exosomes have been discovered to be present in human pericardial fluid (PF). Novel studies have shown characteristic human PF miRNA compositions associated with cardiac diseases and higher miRNA expressions in PF compared to peripheral blood. Five key studies found differentially expressed miRNAs in HF, angina pectoris, aortic stenosis, ventricular tachycardia, and congenital heart diseases with either atrial fibrillation or sinus rhythm. As miRNA-based therapeutics for cardiac fibrosis and HF showed promising results in several in vivo studies for multiple miRNAs, we hypothesize a potential role of miRNA-based therapeutics delivered through the pericardial cavity. This is underlined by the favorable results of the first phase 1b clinical trial in this emerging field. Presenting the first human miRNA antisense drug trial, inhibition of miR-132 by intravenous administration of a novel antisense oligonucleotide, CDR132L, established efficacy in reducing miR-132 in plasma samples in a dose-dependent manner. We screened the literature, provided an overview of the miRNAs and exosomes present in PF, and drew a connection to those miRNAs previously elucidated in cardiac fibrosis and HF. Further, we speculate about clinical implications and potential delivery methods.

An overview of human pericardial space and pericardial fluid

The pericardium is a double-layered fibro-serous sac that envelops the majority of the surface of the heart as well as the great vessels. Pericardial fluid is also contained within the pericardial space. Together, the pericardium and pericardial fluid contribute to a homeostatic environment that facilitates normal cardiac function. Different diseases and procedural interventions may disrupt this homeostatic space causing an imbalance in the composition of immune mediators or by mechanical stress. Inflammatory cells, cytokines, and chemokines are present in the pericardial space. How these specific mediators contribute to different diseases is the subject of debate and research. With the advent of highly specialized assays that can identify and quantify various mediators we can potentially establish specific and sensitive biomarkers that can be used to differentiate pathologies, and aid clinicians in improving clinical outcomes for patients.

Access routes, devices and guidance methods for intrapericardial delivery in cardiac conditions

Drug deposition into the intrapericardial space is favourable for achieving localised effects and targeted cardiac delivery owing to its proximity to the myocardium as well as facilitating optimised pharmacokinetic profiles and a reduction in systemic side effects. Access to the pericardium requires invasive procedures but the risks associated with this have been reduced with technological advances, such as combining transatrial and subxiphoid access with different guidance methods. A variety of introducer devices, ranging from needles to loop-catheters, have also been developed and validated in pre-clinical studies investigating intrapericardial delivery of therapeutic agents. Access techniques are generally well-tolerated, self-limiting and safe, although some rare complications associated with certain approaches have been reported. This review covers these access techniques and how they have been applied to the delivery of drugs, cells, and biologicals, demonstrating the potential of intrapericardial delivery for treatments in cardiac arrhythmia, vascular damage, and myocardial infarction.

Possible mechanism of late lumen enlargement after treatment for de novo coronary lesions with drug-coated balloon

BACKGROUND

Drug-coated balloon (DCB) treatment for de novo coronary artery disease has demonstrated late lumen enlargement (LLE) in mid-term follow-up and it was considered as clinical benefit; however, its mechanism and the predictive factor remains unclear.

METHODS

This study enrolled 46 consecutive patients (54 lesions) treated with DCB, using intravascular ultrasound (IVUS) at the index procedure and at the 9-month follow-up. We measured IVUS parameters at 1-mm intervals and calculated the mean volume of the external elastic membrane (EEM), lumen, and plaque. We calculated the dissection index (DI) defined as summation of the following points, 2: dissection over EEM, 1: intra-EEM dissection, 0: no dissection at every 1-mm interval, and divided by lesion length.

RESULTS

IVUS showed that there was no flow limiting dissection just after DCB treatment, the mean EEM and lumen volume (LV) had significantly increased while mean plaque volume had significantly decreased at 9 months, and 74.1% lesions exhibited LLE. We divided the patients into three groups according to delta mean LV. Mean EEM volume significantly increased and mean plaque volume significantly decreased in the larger and smaller LLE groups, but not in the non-LLE group. The DI was higher in a descending order in the three groups. The multiple regression analysis demonstrated that the DI was the strongest predictor of the change in mean LV.

CONCLUSIONS

LLE after DCB treatment may be caused by vessel enlargement and plaque regression. The non-flow limiting larger dissection just after DCB treatment may strongly associate with the intending LLE.

Technologies for intrapericardial delivery of therapeutics and cells

The pericardium, which surrounds the heart, provides a unique enclosed volume and a site for the delivery of agents to the heart and coronary arteries. While strategies for targeting the delivery of therapeutics to the heart are lacking, various technologies and nanodelivery approaches are emerging as promising methods for site specific delivery to increase therapeutic myocardial retention, efficacy, and bioactivity, while decreasing undesired systemic effects. Here, we provide a literature review of various approaches for intrapericardial delivery of agents. Emphasis is given to sustained delivery approaches (pumps and catheters) and localized release (patches, drug eluting stents, and support devices and meshes). Further, minimally invasive access techniques, pericardial access devices, pericardial washout and fluid analysis, as well as therapeutic and cell delivery vehicles are presented. Finally, several promising new therapeutic targets to treat heart diseases are highlighted.

Nanoparticles administered intrapericardially enhance payload myocardial distribution and retention

Pharmacological therapies for cardiovascular diseases are limited by short-term pharmacokinetics and extra-cardiac adverse effects. Improving delivery selectivity specifically to the heart, wherein therapeutic drug levels can be maintained over time, is highly desirable. Nanoparticle (NP)-based pericardial drug delivery could provide a strategy to concentrate therapeutics within a unique, cardiac-restricted compartment to allow sustained drug penetration into the myocardium. Our objective was to explore the kinetics of myocardial penetration and retention after pericardial NP drug delivery. Fluorescently-tagged poly(lactic-co-glycolic acid) (PLGA) NPs were loaded with BODIPY, a fluorophore, and percutaneously administered into the pericardium via subxiphoid puncture in rabbits. At distinct timepoints hearts were examined for presence of NPs and BODIPY. PLGA NPs were found non-uniformly distributed on the epicardium following pericardial administration, displaying a half-life of ~2.5days in the heart. While NPs were mostly confined to epicardial layers, BODIPY was capable of penetrating into the myocardium, resulting in a transmural gradient. The distinct architecture and physiology of the different regions of the heart influenced BODIPY distribution, with fluorophore penetrating more readily into atria than ventricles. BODIPY proved to have a long-term presence within the heart, with a half-life of ~7days. Our findings demonstrate the potential of utilizing the pericardial space as a sustained drug-eluting reservoir through the application of nanoparticle-based drug delivery, opening several exciting avenues for selective and prolonged cardiac therapeutics.

Future Developments in Nonsurgical Epicardial Therapies

The unique anatomic position of the pericardium in juxtaposition to central cardiac structures enables it to serve as the ideal vantage point for the delivery of novel cardiovascular therapies. Development of new tools to permit delivery of therapy in the closed pericardial space holds promise for near-surgical access to the heart, without open surgical morbidity. Early observations raise hope for the availability of epicardial leads to enhance cardiac resynchronization therapy designed for subxiphoid nonsurgical percutaneous delivery. Emerging technologies for left atrial appendage ligation may offer new strategies for preventing stroke.

The Pericardial Space: Obtaining Access and an Approach to Fluoroscopic Anatomy

The pericardial space is now increasingly used as a means and vantage point for mapping and ablating various arrhythmias. In this review, present techniques to access the pericardial space are examined and potential improvements over this technique discussed. The authors then examine in detail the regional anatomy of the pericardial space relevant to the major arrhythmias treated in contemporary electrophysiology. In each of these sections, emphasis is placed on anatomic fluoroscopic correlation and avoiding complications that may result.

Stability of an autologous platelet clot in the pericardial sac: An experimental and clinical study

OBJECTIVE

Autologous platelet clots serve as slow-release delivery systems for platelet-derived growth factors and cytokines. Their application to the pericardial sac might facilitate salvage and repair of ischemically injured myocardium. However, little is known about platelet clot stability in the pericardial sac. We investigated the stability of platelet clots in vitro and after administration to the pericardial sac in pigs and patients.

METHODS

In 5 Yorkshire-Landrace pigs and 10 patients, in vitro manufactured autologous platelet gel (Medtronic Magellan Platelet Separator) and platelet-rich fibrin (Vivolution Vivostat System) were administered to the pericardial sac for 30 minutes. Two antifibrinolytics (tranexamic acid and aprotinin) were tested for their capacity to stabilize autologous platelet gel. In vitro clots, incubated at 37 degrees C for 48 hours, served as controls. Clot weight was measured before and after administration.

RESULTS

In vitro, autologous platelet gel clots of either formula liquefied almost entirely within 60 minutes whereas platelet-rich fibrin clots remained intact. In the pig, platelet clot weight decreased to 16.7% +/- 7.8% (P < .05) and 66.4% +/- 3.2% (P < .05) of initial clot weight for autologous platelet gel and platelet-rich fibrin, respectively. Addition of antifibrinolytics to autologous platelet gel did not reduce clot degradation significantly. In patients, autologous platelet gel and platelet-rich fibrin clot weight remained 9.0% +/- 1.5% (P < .05) and 73.7% +/- 2.6% (P < .05) of initial clot weight, respectively.

CONCLUSIONS

Autologous platelet gel is unstable both in vitro and in vivo, whereas platelet-rich fibrin remains intact in vitro and, compared with autologous platelet gel, is less subject to degradation in pigs and in patients.

Pericardial disease and pericardial tamponade

The pericardium serves many important functions, but it is not essential for life. Pericardial heart disease comprises only pericarditis and its complications, tamponade and constriction, and congenital lesions. However, the pericardium is affected by virtually every category of disease. The critical care physician is thus likely to encounter the patient with pericardial disease in a variety of settings, either as an isolated phenomenon or as a complication of a variety of systemic disorders, trauma, or certain drugs. Echocardiography is the primary tool for diagnosing and quantifying pericardial effusions, and in the context of the clinical presentation, a thorough understanding of M-mode, two-dimensional, and Doppler findings can help not only to identify patients with impending tamponade, but also to suggest a diagnosis of constrictive pericarditis. This article reviews the pathogenesis and diagnosis of pericardial heart disease, focusing on the diagnostic utility of echocardiography, with an emphasis on those areas of greatest interest to the intensivist.

Dose model for stent-based delivery of a radioactive compound for the treatment of restenosis in coronary arteries

Radiolabeled drug-eluting stents have been proposed recently as a novel method to potentially reduce restenosis in coronary arteries. A P-32 labeled oligonucleotide (ODN) loaded on a polymer coated stent is slowly released in the arterial wall to deliver a therapeutic dose to the target tissue. However, the relatively low proportion of drugs transferred to the arterial wall (<2%-5% typically) raises questions about the degree to which radiolabeled drugs eluted from the stent can contribute to the total radiation dose delivered to tissues. A three-dimensional diffusion-convection transport model is used to model the transport of a hydrophilic drug released from the surface of a stent to the arterial media. Large drug concentration gradients are observed near the stent struts giving rise to a nonuniform radiation activity distribution for the drug in the tissues as a function of time. A voxel-based kernel convolution method is used to calculate the radiation dose rate resulting from this activity build-up in the arterial wall based on the medical internal radiation dose formalism. Measured residence time for the P-32 ODN in the arterial wall and at the stent surface obtained from animal studies are used to normalize the results in terms of absolute dose to tissue. The results indicate that radiation due to drug eluted from the stent contributes only a small fraction of the total radiation delivered to the arterial wall, the main contribution coming from the activity that remains embedded in the stent coating. For hydrophilic compounds with rapid transit times in arterial tissue and minimal binding interactions, the activity build-up in the arterial wall contributes only a small fraction to the total dose delivered by the P-32 ODN stent. For these compounds, it is concluded that radiolabeled drug-eluting stent will not likely improve the performance of radioactive stents for the treatment of restenosis. Also, variability in the delivery efficacy of drug delivery devices makes accurate dosimetry difficult and the drug washout in the systemic circulatory system may yield an unnecessary activity build-up and dose to healthy organs.

Feasibility study and dosimetric assessment of radiolabeled drugs injected to the coronary arterial wall to prevent restenosis

PURPOSE

Intramural delivery of a P-32 radiolabeled oligonucleotide (ODN) using an infiltrating catheter has been proposed recently to potentially reduce restenosis in coronary arteries and tested on a limited number of human subjects. However, because of the low efficiency of drug retention (approximately 2-5%) after the initial washout period from this technique, the dose levels to nontarget organs may be significant and thus may require a detailed investigation. The radiation dose distributions resulting from this technique is investigated using the MIRD formalism and Monte Carlo calculations.

MATERIALS AND METHODS

The total activity of the P-32 ODN to be injected during treatment to deliver a therapeutic dose of approximately 30 Gy to the arterial wall is estimated taking into account the drug delivery efficacy of the infiltrating device (approximately 2-5% typical). Using pharmacokinetic data for P-32 ODN, we estimate the dose to healthy organs resulting from the systemic fraction that is released into the circulatory system during washout (>95% typical). Variabilities in the biological parameters are also identified as important sources of error in the prescribed dose.

RESULTS

A limitation to this technique is the poor accuracy in delivering the prescribed dose due to variability in the amount of drug delivered. Dose to organs is also an important limitation. For example, our calculation indicate that approximately 37 MBq (1 mCi) of P-32 labeled ODN are needed to deliver 30 Gy to the arterial wall assuming a delivery efficiency of 2-5% and a 24-h residence time. This may result in doses of approximately 1 Gy to the spleen and 0.2-0.4 Gy to the liver, kidneys and lungs (95% confidence interval).

CONCLUSION

This novel therapy suffers from serious limitations. It is doubtful that a therapeutic dose can be delivered accurately, safely and effectively to the arterial wall because of the poor delivery efficacy and extreme variability found in drug delivery experiments. Also, dose levels to healthy organs appears to be too high to recommend the use of this technique in human experiments.

Elevated interleukin-1beta in pericardial fluid of patients with ischemic heart disease

BACKGROUND

Inflammatory cytokines may play an important role in the pathogenesis of atherosclerosis and heart failure. We have previously demonstrated that long-term treatment with interleukin (IL)-1beta in the coronary artery and myocardium promotes coronary arteriosclerosis and impairs cardiac function, respectively. The cytokines in pericardial fluid may reflect the extent of coronary atherosclerosis and may also directly promote the atherosclerotic process. This study was designed to examine the significance of cytokine concentrations in pericardial fluid of patients with cardiovascular disease.

METHODS

We measured concentrations of 10 major cytokines in the pericardial fluid of 56 consecutive patients obtained during open heart surgery, 27 with ischemic heart disease (IHD group), 21 with valvular heart disease (VHD group) and eight with congenital heart disease (CHD group).

RESULTS

The pericardial concentrations of IL-1beta (pg/ml) were significantly higher in the IHD group (60 +/- 15) than in the VHD (29 +/- 5) or the CHD group (26 +/- 4) (P < 0.05 both). There was no significant difference in pericardial concentrations of other cytokines among the three groups. In the IHD group, the IL-1beta concentrations were significantly elevated in patients who had undergone emergency operations or in those with unstable angina.

CONCLUSIONS

These results suggest that pericardial concentrations of IL-1beta may reflect the extent of ischemic heart disease and that elevated IL-1beta concentrations in pericardial fluid may also directly promote the process of coronary atherosclerosis.

Transatrial access to the normal pericardial space for local cardiac therapy: preclinical safety testing with aspirin and pulmonary artery hypertension

The reliability, rapidity, and safety of nonsurgical, transatrial pericardial access for local cardiac therapy have been demonstrated in healthy animals. Since many patients take aspirin or have increased right-sided pressures, we evaluated the procedure's safety under these conditions. Transatrial pericardial access was performed in anesthetized pigs following aspirin administration (162 mg p.o., n = 6) or during experimental pulmonary artery hypertension (n = 4 different animals) and required only 3 minutes following guide catheter positioning. Platelet aggregability testing with arachidonic acid confirmed aspirin effectiveness. Mean pericardial fluid hematocrit was 0.1 +/- 0.1% after 2 days of aspirin therapy and 1.9 +/- 1.1% at sacrifice 24 hours later (NS). Mean pericardial fluid hematocrit was 1.0 +/- 0.5% after 45 minutes of pulmonary artery hypertension and 4.3 +/- 0.8% at sacrifice 30 minutes later (NS). Histologic analysis in both groups revealed a small thrombus and localized inflammation at the site of puncture. Neither aspirin use nor pulmonary artery hypertension causes significant bleeding into the pericardial space following transatrial access and thus does not preclude this route for local cardiac drug delivery.

Efficacy of intracoronary versus intravenous FGF-2 in a pig model of chronic myocardial ischemia

BACKGROUND

Therapeutic angiogenesis in ischemic myocardium has been shown to be a feasible and effective strategy to improve regional blood flow and myocardial function. However, the optimal mode of growth factor administration still needs to be established.

METHODS

Using a pig model of chronic myocardial ischemia, we evaluated the efficacy of intravenous and intracoronary infusion of FGF-2 at 2 and 6 microg/kg compared with a vehicle control. Improvement in myocardial perfusion and function was assessed by angiography, colored microspheres, and function and perfusion magnetic resonance imaging.

RESULTS

Intracoronary 6-microg/kg FGF-2 increased angiographic collaterals (p = 0.046) and increased regional blood flow to the ischemic area from 0.36 +/- 0.07 to 0.59 +/- 0.08 mL/min/g at stress (vs control, p = 0.032). Also, after 6 microg/kg intracoronary FGF-2, ejection fraction, regional wall motion, and thickening improved significantly by 9.9% +/- 1.9%, 126% +/- 39%, and 13.8% +/- 3.6%, respectively. Intravenous FGF-2 and intracoronary 2 microg/kg FGF-2 were ineffective.

CONCLUSIONS

A single 6-microg/kg intracoronary treatment with FGF-2 resulted in significant improvement in collateralization and regional and global function of chronically ischemic myocardium. Single intravenous infusion of FGF-2 was not effective in this model.

Intrapericardial paclitaxel delivery inhibits neointimal proliferation and promotes arterial enlargement after porcine coronary overstretch

BACKGROUND

Catheter-based intrapericardial (IPC) delivery of therapeutic agents has recently been demonstrated. Paclitaxel is known to inhibit vascular smooth muscle cell proliferation. This study examined the effect of IPC instillation of paclitaxel on neointimal proliferation after balloon overstretch of porcine coronary arteries.

METHODS AND RESULTS

Overstretch injury of coronary arteries was followed by IPC administration of micellar paclitaxel at low dose (LD, 10 mg; n=6) or high dose (HD, 50 mg; n=7) or of control micelles (50 mg, n=5). Animals were euthanized 28 days after balloon dilation. Arterial injury indices were no different among the groups. The neointimal area, maximal intimal thickness, and adventitial thickness were significantly reduced in both LD (0.47+/-0.04 mm(2), 0.43+/-0.03 mm, and 0.35+/-0.02 mm, respectively) and HD (0.51+/-0.06 mm(2), 0.42+/-0.03 mm, and 0. 38+/-0.03 mm, respectively) paclitaxel groups compared with the control group (0.79+/-0.07 mm(2), 0.56+/-0.02 mm, and 0.47+/-0.02 mm, respectively; P:<0.001). Meanwhile, the vessel circumference measured at the external elastic lamina of paclitaxel-treated vessels was significantly larger than the control circumference. Apoptotic cells were found in the neointima. The apoptotic cell percentage was not different between the control (1.72%) and LD (2. 31%) groups but was higher in the HD group (7.07%, P:<0.0001 versus control and LD groups). Immunostaining for matrix metalloproteinase-2 revealed concurrent reduction in the HD group compared with the control and LD groups.

CONCLUSIONS

IPC space delivery of a single dose of paclitaxel significantly reduces vessel narrowing in this balloon-overstretch model. This effect is mediated by reduction of neointimal mass as well as positive vascular remodeling.

Gene therapy for myocardial angiogenesis: has it come of age?

Vasculogenesis and angiogenesis are the processes responsible for the development of the circulatory system during embryonic and adult life. Vasculogenesis occurs during embryogenesis while angiogenesis refers to blood vessel formation from any preexisting vasculature. Postnatal angiogenesis resumes during reproduction, wound healing, and ischemia. Excess blood vessel formation may contribute to initiating and maintaining many diseases such as chronic inflammatory disorders, tumor growth, restenosis, and atherosclerosis. In contrast. insufficient blood vessel formation is responsible for tissue ischemia, as in coronary artery disease. An increasing number of patients with advanced coronary artery disease remain symptomatic despite maximal interventional, surgical or medical treatment. Ideally, they would benefit most from additional arterial blood supply to ischemic areas of myocardium. Therapeutic angiogenesis, the ability to induce the growth of new blood vessels, is one of the most intriguing new frontiers in interventional cardiology for this growing patient group. Several approaches are currently undergoing intensive experimental investigations or have already entered early clinical trials involving either local angiogenic peptide administration or the transfection of angiogenic genes. Gene therapy for therapeutic myocardial angiogenesis is the most promising synthesis of two emerging technologies. In the following article, we will review the fundamental pathophysiological concepts of gene-based angiogenic therapy, the technical approaches and delivery systems, and the results of the first clinical trials. We will also discuss the controversies and unresolved issues of this new revascularization therapy.

Preclinical safety testing of percutaneous transatrial access to the normal pericardial space for local cardiac drug delivery and diagnostic sampling

The safety of a percutaneous method and streamlined catheter system to access the normal pericardial space via the right atrial appendage for drug delivery and diagnostic sampling was demonstrated in 20 anesthetized pigs. Access was successfully accomplished in all animals within 3 min of guide catheter positioning and was documented by fluoroscopic imaging and pericardial fluid sampling. The animals were sacrificed at 24 hr (n = 10) and 2 weeks (n = 10) for histopathologic analysis. Mean pericardial hematocrit was 1.1% +/- 0.3% at initial sampling, 4.3% +/- 1.4% at 24 hr (P = 0.005 vs. baseline), and 0.4% +/- 0.2% at 2 weeks (P = 0.13 vs. baseline). At 24 hr, there was local inflammatory reaction in the atrial wall and a small thrombus at the site of puncture. At 2 weeks, no significant inflammatory changes or pericarditis were evident. The technique is well tolerated with no apparent adverse complications. Advances in intrapericardial therapeutics and diagnostics will direct the clinical application of this novel approach in human subjects.